The invention relates to a method for sorting wafers from an initial state, in which the wafers are arranged in any desired sequence in compartments of a holding device, to an end state in which the wafers are arranged in accordance with a prescribed sequence, as much as possible, in the compartments of the holding device. The wafers are identifiable as elements of a finite sequence based on an information carrier.
It is known, for example from U.S. Pat. No. 5,225,691, to transport wafers of a chip production operation in what are known as tray cassettes, in order to protect the sensitive wafers. The wafers are in this case stored in individual slots of the tray cassette in such a way that they can be easily removed by machine (for example by a robot). Each of the wafers has an information carrier (for example a barcode), which contains, for example, the association with a specific batch and a consecutive number as an identification feature.
The wafers are regularly removed during chip production for further processing of the tray cassettes. For this purpose it is frequently necessary to bring the wafers of the tray cassette into a specific sequence (for example into the correct sequence of the identification features).
Devices are known for this type of handling of the wafers, such as for example, the sorting system taught in U.S. Pat. No. 6,213,708.
It is also known to use what are known as two-cassette mappers, in order to sort wafers from one tray cassette into another tray cassette or within a tray. In this case, the sorting takes place in two steps. In the first step, all of the wafers are pulled one after the other by a robot, a barcode as an information carrier is read by a device (aligner), and after being intermediately deposited, a wafer is pushed back into the original slot of the tray cassette. In a second step, the wafers are rearranged into the correct slots based on the information of the identified wafer numbers read from the barcode.
If barcodes of some wafers cannot be identified, they are initially pushed back into the original slot and the sorting operation is continued for the remaining wafers. At the end, a machine-based inspection of the non-identified wafers is performed by a member of staff. The two steps involved in sorting make the overall sorting time considerably longer.
The present invention is based on providing a method and a device with which the number of reading operations on information carriers and the number of wafer movements are as small as possible.
The object of the invention is based on a method for sorting wafers of a chip production operation from an initial state into an end state. The method includes steps of:
providing the wafers in the initial state such that the wafers are arranged in a given sequence in compartments of a holding device;
enabling the wafers to be at least partly identified as elements of a finite sequence based on information carriers; and
sorting the wafers into the end state in which each wafer is arranged, as much as possible in accordance with a prescribed sequence, in the compartments of the holding device by:
removing a first wafer from a first compartment of the holding device,
with a reading device, reading an information carrier of the first wafer to determine a position of the first wafer in the prescribed sequence,
subsequently, removing a second wafer from a second compartment corresponding to the position of the first wafer in the prescribed sequence, and
moving the first wafer into a compartment corresponding to the position of the first wafer in the prescribed sequence.
The object of the invention is also based on a wafer sorting apparatus including: a data processing device for controlling the above-described method for sorting the wafers of the chip production operation from the initial state into the end state; at least one device for moving at least the first wafer and the second wafer; and a reading device for reading the information carrier of the first wafer.
According to the invention, a first wafer is removed from a first compartment of the holding device and the information carrier of the first wafer is read by a reading device to determine the position of the first wafer in a finite sequence. Consequently, it is ascertained, for example, which number the first wafer has in the sequence of all the wafers in a holding device.
Subsequently, a second wafer is removed from a second compartment, the second compartment corresponding to the position of the first wafer in the sequence. Consequently, space for the first wafer is created. The first wafer is then moved into the second compartment, which corresponds to its position in the sequence.
This direct sorting eliminates identifying all of the wafers, in order to subsequently to perform sorting. According to the invention, a two-step strategy is transformed into a direct sorting. This allows the sorting time to be shortened considerably.
It is advantageous in this case if the sequence in the end state corresponds to the sequence of an identification number of the wafer. Since wafers generally have such numbering, it is particularly easy to provide sorting in this sequence.
Under certain circumstances it may be advantageous if the sequence of the wafers in the end state deviates from the sequence of the identification numbers. Consequently, for example, a table with a desired sorting sequence may be prescribed as the sequence and the inventive method sorts the wafers according to this sequence.
A refinement of the method is particularly advantageous and includes, if a wafer has a non-readable information carrier, in particular a non-readable barcode, this wafer in the end state of the sorting is arranged in a compartment of the holding device which is not occupied by a wafer with a readable information carrier. It is ensured by the direct sorting that the non-readable wafers are identified and sorted into their appropriate positions.
It is particularly advantageous in this case if the compartment, in which a wafer with a non-readable information carrier is arranged, is automatically provided with a marking. Consequently, an operator can easily identify in which compartment a wafer with a non-readable information carrier lies.
Furthermore, it is advantageous if each wafer which has a non-readable information carrier is provided with a flag for non-readability by a program of a data processing device. A flag is understood here as meaning a programming identification that can assume only two states. For example, the flag is set if the information carrier is non-readable, and the flag is not set if the information carrier is readable.
The inventive device includes: at least one device for moving at least one wafer; a reading device for an information carrier of the wafer; and a data processing device for controlling the procedure of the method. The invention is explained in more detail below on the basis of several exemplary embodiments with reference to the figures of the drawings.